Flora of Clark Valley Area


Flora of Clark Valley Area

This checklist is a start at a flora of the Clark Valley Area. It consists of 157 taxa. Of those 157 taxa, we observed 121 in five different field surveys, and 110 of the 157 taxa have been vouchered here.

The checklist is current as of 30 December 2016, but the following text is from a previous version of this page done in the year 2008.

The floristic area denoted as the Clark Valley Area is delineated by the region outlined in red in the following map:

Only a single road traverses this area, the Rockhouse Canyon Road, on the western side of the Valley (see map below). There is also a private road that accesses private land on the north side of Clark Lake.

The western boundary of this area is the ridgeline / drainage divide of Coyote Mountain and its extension northward, to include the entire drainage basin of Butler Canyon / Rockhouse Canyon up to the San Diego County border with Riverside County.

The eastern boundary is mostly at the 3000 foot elevation contour of the Santa Rosa Mountains. The southeastern boundary is placed just a bit to the west of the Villager Peak Trail and Rattlesnake Canyon, since those two areas are more naturally included in the neighboring floristic area.

The southern boundary is set along Highway S22 to divide Clark Valley from the Badlands. Although this boundary is somewhat arbitrary, S22 gives a well-defined boundary.

For more information about Clark Valley, including pictures from our surveys, see Borrego Desert: Clark Valley.

Voucher Records

The voucher search was redone on 24 December 2016. This time only vouchers from Clark Valley itself and the immediately-surrounding areas were accepted. The following text has not been changed from the previous search.

The vouchers come from a search on 8 December 2008 of the Consortium of California Herbaria. The Consortium records were searched for San Diego County specimens that contained the word Clark in the locality (297 vouchers), as well as records with coordinates that fell within a rectangle that encompassed this area (369 vouchers). Duplicate vouchers, vouchers outside this area, and vouchers determined only to the genus that had more than one possible species, were removed.

This process yielded a total of 226 vouchers of 133 unique taxa.

The dominant collectors in the Consortium records were Larry Hendrickson and Kim Marsden and vice-versa, 83 vouchers; R. Mitchel Beauchamp, R. C. Pierce, 71 vouchers; and Bill Sullivan, 31 vouchers. These three sets of collectors accounted for 185 of the 226 vouchers, 82% of the total.

The locations of the vouchers are plotted in the following map, which also shows the boundaries of this region in more detail:

Because many vouchers share the same location, there are far fewer than 226 points plotted above.

Field Work

Field work has been added from 3/7/09 and 12/19/09, but the following text has not yet been updated.

Three different areas within the Clark Valley area have been field surveyed. On 27 December 2007, James Dillane, Wayne Armstrong and I surveyed the 2.7 miles of the Alcoholic Pass Trail on Coyote Mountain that are on the Clark Valley side. We surveyed only for species not previously found on the southwestern side of the trail, so this survey was very incomplete. That portion of the trail is shown in green on the following map:

On 9 and 12 December 2008, Mike Crouse and I surveyed the two different routes shown in the following map :

We surveyed 5.75 unique miles on 9 December 2008, and 5.7 unique miles on 12 December 2008.

We also scanned the slopes of the nearby portion of the Santa Rosa Mountains for the elephant trees, Bursera microphylla, reported from that location (indicated by the labeled line in the above map), without finding them. However, since those trees were likely to be leafless at that time, they easily could have escaped our binocular survey from afar. This species was added to the checklist below based on sightings by Mark Jorgensen and Larry Hendrickson.

Note added 30 December 2016: We relocated the elephant trees on 19 December 2009 and vouchered one of them; see The Elephant Trees of Clark Valley.

A total of 63 taxa that could be fairly-confidently identified were found in those three December searches; 19 of those 63 taxa, 30%, are not among the vouchered species. A small number of additional taxa were found that could not be confidently identified at those times.

The unvouchered species do not come from any general problem with my identifications, since those unvouchered species include such easy-to-recognize taxa as Opuntia ramosissima, Psorothamnus spinosus, Ferocactus cylindraceus, and Encelia farinosa. This simply reflects the lack of botanical work for this area. It is possible that one or two of the unvouchered species might be misdetermined, since some of those determinations were made from dead plants.

Total Checklist

The total number of taxa presented below is 153, 148 of which are native. Of the 153 taxa, 63 were observed on one of the three field surveys, leaving 90 to be found from surveys at a more optimal time of year, or in locations not yet surveyed. Since 30% of the observed taxa are so far unvouchered, this may imply that the voucher list is on the order of 30% incomplete. However, since many of the unvouchered taxa are common, it may only imply that the most common taxa have not yet been vouchered.

Another source of incompleteness for this checklist is that most of the area has never been surveyed, especially the steep lower slopes of the Santa Rosa Mountains which may defy further surveys indefinitely. I estimate at most 24 square miles (62 km2) has had any survey within it, whereas 34 square miles (88 km2) has never had any survey within it. Using the standard relationship that the number of species scales as the 0.3 power of the area, this implies that (58/24)0.3 = 1.30 times more species should be found in the total area of ~58 square miles. This incompleteness is an additional factor to the incompleteness of the surveyed areas.

Thus the checklist below may be on the order of 1 / 1.32 ~ 60% complete, implying that the true number of taxa in this area might be roughly 260 instead of the 153 present below.

Checklist for the Clark Valley Area

This checklist is current as of 30 December 2016.

This checklist is only for a subset of the Clark Valley Floristic Area defined above, of just the floor of the Valley and the immediately-adjacent areas. Rockhouse Canyon / Butler Canyon has its own flora since that area is very different floristically from the desert floor area.


An asterisk before the common name indicates a non-native species.

The column with header #V gives the number of vouchers in this area.

The column with header #Pls gives the minimum number of observed plants from all the surveys in this area, up to a maximum of 99 plants. An x indicates we have observed that taxon but no abundance estimate was made.

One species, Helianthus niveus ssp. tephrodes, has no entry in either column since it may or may not be present in this area. One voucher from 1933 has a vague location of North Borrego Valley on road to Clark Lake. Another voucher is from just east of this area on S22.

Version for printing, without lines and other text on this page: html (4 pages) or pdf Clickbook booklet (1 double-sided page). (See printing instructions for an explanation of these options)

#FamScientific Name(*)Common Name#V#Pls
1PteCheilanthes parryiwoolly lipfern 10
2AcaJusticia californicachuparosa1x
3AmaAmaranthus blitoides*mat amaranth 20
4AmaAmaranthus fimbriatusfringed amaranth1 
5AmaTidestromia suffruticosa var. oblongifoliaArizona honeysweet 15
6ApoAsclepias subulatarush milkweed12
7ApoFunastrum hirtellumrambling milkweed1 
8ApoPilostyles thurberiThurber's pilostyles31
9AstAmbrosia dumosaburroweed599
10AstAmbrosia salsola var. salsolacheesebush35
11AstBaileya pauciradiataColorado Desert marigold579
12AstBebbia juncea var. asperasweetbush24
13AstCalycoseris parryiyellow tackstem1 
14AstCalycoseris wrightiiwhite tackstem1 
15AstChaenactis carphoclinia var. carphocliniapebble pincushion2 
16AstChaenactis fremontiiFremont pincushion220
17AstChaenactis stevioidesdesert pincushion 99
18AstDicoria canescensdesert dicoria120
19AstEncelia farinosabrittlebush420
20AstEncelia frutescensbutton encelia22
21AstGeraea canescenshairy desert-sunflower499
22AstHelianthus niveus ssp. tephrodesAlgodones Dunes sunflower  
23AstHelianthus petiolaris ssp. canescensgray desert sunflower2 
24AstIsocoma acradenia var. acradeniaentire-leaved alkali goldenbush2 
25AstIsocoma acradenia var. eremophilatoothed-leaved alkali goldenbush199
26AstLepidospartum squamatumscale-broom1 
27AstMalacothrix glabratadesert dandelion230
28AstMonoptilon bellioidesdesert star1x
29AstPalafoxia arida var. aridaSpanish needle740
30AstPerityle emoryiEmory's rock-daisy1 
31AstPeucephyllum schottiipygmy-cedar x
32AstPluchea sericeaarrow-weed 99
33AstPsathyrotes ramosissimaturtleback x
34AstRafinesquia neomexicanadesert chicory299
35AstStephanomeria exigua ssp. exiguaslender wreathplant1 
36AstStephanomeria pauciflorawire-lettuce 1
37AstTrichoptilium incisumyellow-head1 
38AstTrixis californica var. californicaCalifornia trixis 1
39AstXylorhiza orcuttiiOrcutt's woody-aster3 
40BigChilopsis linearis ssp. arcuatadesert-willow3 
41BorAmsinckia tessellata var. tessellatabristly fiddleneck1 
42BorCryptantha angustifolianarrow-leaved cryptantha799
43BorCryptantha barbigera var. barbigerabearded cryptantha 1
44BorCryptantha costataribbed cryptantha4 
45BorCryptantha ganderiGander's cryptantha x
46BorCryptantha maritimaGuadalupe cryptantha 5
47BorCryptantha micrantha var. micranthared-root cryptantha2 
48BorCryptantha nevadensis var. nevadensisNevada cryptantha x
49BorHeliotropium curassavicum var. oculatumseaside heliotrope2x
50BorPectocarya heterocarpachuckwalla pectocarya210
51BorPectocarya peninsularisBaja pectocarya1 
52BorPectocarya platycarpabroad-fruited combseed 1
53BorPectocarya recurvatacurvenut combseed1 
54BorPhacelia crenulata var. ambiguaheliotrope phacelia120
55BorPhacelia crenulata var. minutifloralittle-flowered heliotrope phacelia 20
56BorPhacelia distanscommon phacelia210
57BorTiquilia palmeriPalmer's coldenia11
58BorTiquilia plicataplicate coldenia1 
59BraBrassica tournefortii*Sahara mustard199
60BraDithyrea californicaspectacle-pod21
61BraLepidium lasiocarpum ssp. lasiocarpumhairy-podded pepper-grass399
62BraSisymbrium irio*London rocket25
63BraStreptanthella longirostrislongbeak streptanthella15
64BurBursera microphyllaelephant tree 13
65CacCylindropuntia bigeloviiteddy-bear cholla x
66CacCylindropuntia echinocarpasilver cholla322
67CacCylindropuntia ganderiGander's cholla 15
68CacCylindropuntia ramosissimapencil cholla120
69CacEchinocereus engelmanniiEngelmann's hedgehog cactus 1
70CacFerocactus cylindraceusCalifornia barrel cactus 8
71CacMammillaria dioicaCalifornia fish-hook cactus 1
72CacOpuntia basilaris var. basilarisbeavertail cactus 1
73CamNemacladus sp.nemacladus x
74CarAchyronychia cooperifrost mat4 
75CheAllenrolfea occidentalisiodine-bush399
76CheAtriplex canescens var. laciniataCaleb four-wing saltbush199
77CheAtriplex elegans var. fasciculatawheelscale210
78CheAtriplex hymenelytradesert holly23
79CheAtriplex lentiformis ssp. lentiformisbig saltbush 65
80CheAtriplex polycarpacattle saltbush 99
81CheMonolepis nuttallianaNuttall's poverty weed199
82CheSalsola paulsenii*Paulsen's Russian thistle199
83CheSuaeda nigrabush seepweed199
84ClePeritoma arboreabladderpod1 
85CleWislizenia refracta ssp. palmeriPalmer's jackass clover1 
86ConCuscuta californica var. papillosapapillate dodder 3
87CroCrossosoma bigeloviirock crossosoma1 
88EupChamaesyce micromeraSonoran spurge11
89EupChamaesyce polycarpasmall-seeded spurge180
90EupChamaesyce setilobastarfish (Yuma) spurge1 
91EupCroton californicusCalifornia croton 3
92EupDitaxis lanceolatanarrowleaf ditaxis x
93EupDitaxis neomexicanaNew Mexico ditaxis1 
94EupStillingia spinulosaannual stillingia720
95FabAcmispon strigosusstrigose lotus 1
96FabAstragalus crotalariaeSalton milk-vetch299
97FabAstragalus didymocarpus var. dispermusdwarf white milk-vetch1 
98FabAstragalus lentiginosus var. borreganusBorrego milk-vetch1399
99FabDalea mollissilky dalea1 
100FabDalea mollissimadowny dalea1x
101FabLupinus arizonicusArizona lupine123
102FabProsopis glandulosa var. torreyanahoney mesquite399
103FabPsorothamnus emoryiEmory's indigo-bush715
104FabPsorothamnus schottiiindigo bush 50
105FabPsorothamnus spinosussmoke tree 1
106FabSenegalia greggiicatclaw 20
107FouFouquieria splendens ssp. splendensocotillo18
108GerErodium cicutarium*redstem filaree110
109GerErodium texanumTexas filaree1x
110KraKrameria bicolorwhite rhatany340
111LamHyptis emoryidesert-lavender210
112LamSalvia columbariaechia 5
113LamSalvia vaseyiVasey's sage 10
114LoaMentzelia affinisyellow blazing star120
115LoaMentzelia desertorumdesert blazing star2 
116LoaMentzelia involucratabracted blazing star 3
117LoaPetalonyx thurberi ssp. thurberiThurber's sandpaper-plant210
118MalEremalche exiliswhite mallow21
119MalEremalche rotundifoliadesert five-spot1 
120MalHibiscus denudatusrock hibiscus x
121MalSphaeralcea angustifoliacopper globemallow199
122MonCistanthe ambiguadead man's fingers199
123NycAbronia villosa var. villosahairy sand-verbena550
124NycAllionia incarnata var. villosalarge-flowered trailing four o'clock1 
125OnaChylismia claviformis ssp. peirsoniibrown-eyed primrose699
126OnaEremothera boothii ssp. condensataBooth's evening primrose27
127OnaEulobus californicusCalifornia suncup299
128OnaOenothera deltoides ssp. deltoidesdune primrose399
129PapEschscholzia minutiflora ssp. minutiflorasmall-flowered poppy x
130PapEschscholzia parishiiParish's poppy x
131PhrMimulus bigelovii var. bigeloviiBigelow's monkeyflower x
132PlaMohavea confertifloraghost flower1 
133PlaPlantago ovatadesert plantain699
134PolAliciella latifolia ssp. latifoliabroad-leaf gilia x
135PolEriastrum eremicum ssp. eremicumdesert woolly-star 5
136PolLoeseliastrum matthewsiidesert calico1 
137PolLoeseliastrum schottiiSchott's calico199
138PolChorizanthe brevicornu var. brevicornubrittle spineflower13
139PolChorizanthe corrugatawrinkled spineflower1x
140PolEriogonum inflatumdesert trumpet1x
141PolEriogonum thomasiiThomas' buckwheat2x
142PolEriogonum trichopeslittle desert trumpet 20
143ResOligomeris linifolialineleaf whitepuff599
144SimSimmondsia chinensisjojoba120
145SolLycium brevipes var. brevipesdesert boxthorn399
146SolNicotiana clevelandiiCleveland's tobacco1 
147TamTamarix aphylla*athel 5
148TamTamarix ramosissima*saltcedar 5
149VisPhoradendron californicumdesert mistletoe 99
150ZygFagonia laevisCalifornia fagonia2x
151ZygFagonia pachyacanthasticky fagonia x
152ZygLarrea tridentatacreosote bush899
153AgaHesperocallis undulatadesert lily250
154PoaAristida adscensionissix-weeks three-awn3 
155PoaHilaria rigidabig galleta280
156PoaSchismus arabicus*Mediterranean grass1 
157PoaSchismus barbatus*Mediterranean schismus499

Voucher data provided by the participants of the Consortium of California Herbaria (ucjeps.berkeley.edu/consortium/)

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Copyright © 2008-2016 by Tom Chester, Mike Crouse, RT and Shaun Hawke, Keir Morse, and John Randall.
Permission is freely granted to reproduce any or all of this page as long as credit is given to me at this source:
Comments and feedback: Tom Chester
Last update: 30 December 2016